Silver halide dispersion



United States Patent 3,392,025 SILVER HALIDE DISPERSION Thomas E.Whiteley and Ernest J. Perry, Rochester, N .Y., assignors to EastmanKodak Company, Rochester, N .Y., a corporation of New Jersey No Drawing.Filed Aug. 24, 1964, Ser. No. 391,787 Claims. (Cl. 96-114) ABSTRACT OFTHE DISCLOSURE For the precipition and emulsification step inpreparation of photographic silver halide emulsions, a new peptizer foruse in the aqueous dispersion is selected from water-soluble polymerscomprising recurring units having the structure where Z is a divalentorganic radical, A and B are selected from amino and carboxyl and theratio of amino to carboxyl is in the range from 1:5 to 1:1.25 and notmore than one of A and B is amino in any one such unit.

This invention relates to silver halide disperssions, and moreparticularly to the method of preparing silver halide dispersions whichinvolves precipitating silver halide in the presence of certainpeptizers.

It is well known that the first step in the preparation of photographicemulsions involves the peptization of sliver halides formed by a doubledecomposition reaction of soluble silver salts and alkali halide salts,either in the presence or the absence of ammonia. Effective peptizationl) prevents the insoluble silver halide from precipitating in the formof coarse crystals, which, because of excessive graininess, would beuseless in photographic emulsion layers; and (2) prevents clumping andaggregation of the emulsion crystals, thus preventing grossirregularities and the occurrence of infectious development in thedeveloped photographic emulsion layers. A further requirement ofeffective peptization is the proper growth of the silver halide emulsioncrystals during preparation of the emulsion since the size distributionsresulting from this growth have a decisive influence on basicsensitomeric properties such as speed, contrast, graininess andacutance.

While gelatin is a satisfactory peptizer, its use has a number ofinherent disadvantages. As a naturally occurring material, it is rathersensitive to bacterial attack and its uniformity is questionable due tothe variety of sources from which it is obtained. The compatibility ofgelatin with other polymeric vehicles which may provide coatings havingsuperior physical properties is also limited. In addition, it isdesirable to be able to obtain emulsion crystals which havephotographically significant differences in crystal structure and sizedistribution as compared to those obtained when gelatin is employed.

Many of the polymers which have heretofore been suggested as peptizersfor silver halide have not functioned satisfactorily. In many instances,they have not produced effective peptization, which results in clumpingand aggregation of the emulsion grains. In other instances, for example,with poly(vinyl alcohol) or polyvinylpyrrolidone, restraint of graingrowth by the peptizer has rendered it impossible to obtain sufficientlylarge, well 3,392,025 Patented July 9, 1968 Too shaped emulsion crystalshaving satisfactory photogrhphic characteristics.

One object of our invention is to provide a method for the preparationof silver halide dispersions. Another object of our invention is toprovide a method for preparing silver halides which features theprecipitation of silver halides in the presence of certain polymericpeptizers. A further object of our invention is to provide silver halidecrystals differing photographically in irregularities and sizedistributions from silver halide crystals obtained when gelatin isemployed as peptizer. Another object of our invention is to providenovel polymers. Other objects of our invention will appear herein.

We have discovered new and highly useful polymers having a carbon chainbackbone and featuring a plurality of amino and carboxyl groups attacheddirectly to separate, adjacent carbon atoms in the polymer backbone. Wehave found that these polymers, having as the critical feature adjacentcarbon atoms substituted with amino and carboxyl groups, are highlyuseful peptizers for silver halide salts.

A particularly useful class of polymers in accordance with our inventioncomprises the following repeating units:

wherein A and B are selected from the group consisting of amino andcarboxyl, the ratio of amino groups to carboxyl groups in the polymer isfrom 10:5 .0 to 1.0: 1.25; and in each repeating unit, not more than oneof A and B is an amino group; and, Z is a divalent organic radical, suchas, ethylene or substituted ethylene radicals wherein one or more of thehydrogen atoms is replaced with one of the following groups: hydroxyl;alkyl, such as methyl or ethyl; or aryl, such as phenyl. These polymersmay be prepared by copolymerizing maleic anhydride with any of thepolymerizable polyolefin (e.g., C=CH groups referred to in Re. 23,514 ofVoss et al. US. Patent 2,047,398 (1936), and selectively convertinganhydried groups in the polymer to amino and carboxyl groups so that notmore than one amino group is present in each repeating unit. Not all theanhydride groups need be converted to amino and carboxyl groups. Also,other substituents in place of amino and carboxyl groups (as A and B inthe above formula) may be present in minor proportions so long as suchsubstituents do not adversely affect the peptizing qualities of thepolymer.

A preferred polymer in accordance with our invention contains thefollowing repeating unit:

wherein A and B are selected from the group consisting of amino andcarboXyl, the ratio of amino groups to carboxyl groups in the polymerbeing from 1.0:5.() to 1.0:1.25, and, in each repeating unit, not morethan one of A and B is an amino group.

The repeating units defined herein may be arranged in random fashion inthe present polymers. For example, the repeating units may be attachedto one another in a head-to-head or tail-to-tail manner.

We have found that the above copolymers are particularly effectivepeptizers in that they promote a very desirable type of emulsion crystalgrain growth. Thus, the

(9 use of the subject copolymers as peptizers results in tabularoctahedral grains in neutral emulsions. These grains are of suflicientlylarge size to provide proper photographic sensitivity. The grain sizedistribution of the silver halide crystals obtained when peptized inaccordance with the invention is distinctively different from that ofsimilarly prepared emulsions which are peptized by gelatin. This isdemonstrated by the relationship between the mean grain area of thesilver halide obtained and a function known to those familiar with theart as the sigma function, which is a measure of the width of the grainsize distribution curve.

The polymeric peptizers of the invention are also useful in thepreparation of ammoniacal emulsions. The emulsion grains obtained are ofcubic crystalline structure, and have a sufiiciently large size topossess the required photographic sensitivity. Ammoniacal emulsions ofunusually high silver halide concentration may be prepared With thepolymeric peptizers of the invention without the occurrence of certaindeposits or sedimentation which may occur during the preparation ofequally high concentrations of silver halide when gelatin is used aspeptizer.

We have further found that the size of the silver halide grain can beregulated to some extent by changes in the ratio of amino groups tocarboxyl groups in the polymeric peptizers of the invention. Changes inthe amino-tocarboxyl ratio of the polymers employed in the inventionresult in morphological characteristic changes in the grains, and inchanges in the rate of solution of silver halide crystals. In addition,distinct changes in the rate of physical development with a constantsilver ion concentration at an effective catalytic surface are observedif the amino-to-carboxyl ratio in the polymers is varied.

Our invention will be further illustrated by Examples 1-12.

EXAMPLE 1 Copoly(ethylene fl-aminoacrylic acid/ethylene maleic acid),amino-carboxyl ratio of 1.0 to 3.0

A solution of 100 g. of low-molecular-weight copoly (ethylene maleicanhydride )in 800 ml. of concentrated sulfuric acid was placed in afive-liter 3-neck flask fitted with a stirrer, a nitrogen inlet, athermometer, and a drying tube. The flask was flushed with nitrogen, andsodium azide (46.5 g.) was introduced at such a rate that thetemperature remained between 40 and 48 C., with external cooling asnecessary. When the sodium azide was completely added and thetemperature no longer rose, the solution was heated to 95 C. for twohours. Ligroin added to the solution controls foaming and facilitatesstirring. The solution was allowed to cool slowly, overnight, and thepolymer precipitated by pouring, in a thin stream, into vigorouslystirred acetone. The finely divided precipitate was washed well withacetone and dried.

The polymer was dissolved in 800 ml. of water and the solution dilutedto two liters. The polymer was reprecipitated by raising the pH to theisoelectric point (approximately pH 2.4). The polymer was washed wellwith water and then acetone and then dried. The yield was 78 g.

Analysis: C, 45.5; H, 6.9; N, 5.3; Na, .3.

A neutral emulsion was prepared in the following manner. An aqueoussolution (20 ml.) of 3.82 g. of silver nitrate was added over a periodof 30 minutes to 30 ml. of an aqueous solution containing 3.275 g. ofpotassium bromide, 0.1 g. of potassium iodide, and 1.0 g. of thecopoly(ethylene fi-amiuoacrylic acid/ethylene maleic acid). The reactionmxiture was kept at 70 C. and stirred continuously. After completeaddition of the silver nitrate, the reaction mixture was stirredcontinuously for an additional ten minutes while the temperature washeld at 70 C. The resultant emulsion showed excellent stability andconsisted of well dispersed tabular octahedral grains including manytriangular shapes with straight edges and sharp corners. The diametersof these grains were in the 4. range 0.333.26 microns, the meangrainarea was 0.996 square micron, the Width of the size distribution curve,expressed in terms of the function known to those skilled in the art asthe sigma function corresponded to a value of sigma equal to 1.634square microns and the number of dislocations per emulsion grain, asdetermined by well known methods of X-ray analysis, was equal to 8.5. Bycomparison, a similarly prepared emulsion peptized by gelatin instead ofcopoly(ethylene fi-aminoacrylic acid/ ethylene maleic acid) was found tohave a mean grain area of 0.826 square micron, the width of the sizedistribution curve corresponded to a sigma of 0.807 square micron, andthe number of dislocations per grain was equal to 9.1. The coefiicientof variation (100 sigma/ mean grain area) was 164.1 for the emulsionpeptized by copoly (ethylene fi-aminoacrylic acid! ethylene maleic acid)and 97.7 for the emulsion peptized by gelatin.

The fact that the colloid-chemical properties of copoly (ethylenefl-aminoacrylic acid/ethylene maleic acid) are such as to permit thecoagulation of emulsion grains by addition of acid, removal of solublesalts by washing and redispersion in a film-forming vehicle, is evidentfrom the following experimental results.

To an emulsion peptized by the copoly(ethylene B- aminoacrylicacid/ethylene maleic acid) polymer there was added a solution of l Nsulfuric acid. Dropwise addition to the stirred emulsion was continueduntil the entire emulsion separated out as a coagulum. The soluble saltswere then washed out of the coagulated emulsion by repeated addition ofwater followed by decantation. The coagulum was then dispersed in watercontaining sufiicient sodium hydroxide to raise the pH level above pH 6.The dispersed emulsion grains Were then stirred into a 9 percent gelatinsolution. The resultant emulsion which contained 4.7 percent silverhalide in the form of Well dispersed grains and 5 percent gelatin wasthen coated on a cellulose acetate support after addition of thecustomary amounts of spreading agent (saponin) and crosslinking agent(formaldehyde). After drying and fixation, the resulting coating wascompletely clear which shows that satisfactory compatibility between thepeptizer, copoly(ethylene B-aminoacrylic acid/ ethylene maleic acid) andthe film-forming vehicle, gelatin, had been attained.

EXAMPLE 2 An ammonical emulsion was prepared in the following manner. Anaqueous solution (20.0 ml.) containing 3.82 g. silver nitrate and anamount of ammonium hydroxide just sufficient to redissolve theprecipitate formed initially on addition of ammonuim hydroxide to thesilver nitrate solution, was added with continuous stirring over aperiod of seconds to 30 ml. of a solution contaning 3.14 g. of potassiumbromide, 0.1 g. of potassium iodide, and 1.0 g. of copoly(ethylenefiaminoacrylic acid/ethylene maleic acid) (amino-carboxyl ratio of 10:30described in Example 1.) Stirring was continued for an additional39-minute period. The temperature of the reaction mixture duringaddition and subsequent stirring was held at 45 C. The resultantemulsion showed excellent stability and consisted of predominantly cubicgrains with diameters in the range 0.50-1.76 microns. The mean grainarea of this emulsion was 1.581 square microns, the width of the sizedistribution curve corresponded to sigma equal to 0.61 square micron,and the number of dislocations per grain was equal to 9.4. Bycomparison, a similarly prepared emulsion for which gelatin was used asthe peptizer, had a mean grain area of 1.048 square microns, the widthof the size distribution curve corresponding to sigma equal to 0.464square micron, the number of dislocations per grain was 6.2. Thecoefiicient of variation, as defined in Example 1, was 38.7 for theemulsion peptized by copoly(ethylene B-aminoacrylic acid/ethylene maleicacid) and 44.2 for the emulsion peptized by gelatin.

EXAMPLE 3 An aqueous solution (20.0 ml.) containing 8.495 g. silvernitrate and suflicient ammonium hydroxide to just dissolve theprecipitate formed initially during addition of ammonium hydroxide tothe silver nitrate solution, was added with continuous stirring over aperiod of 85 seconds to 30.0 ml. of a solution containing 6.98 g.potassium bromide, 0.226 g. potassium iodide, and 1.0 g. ofcopoly(ethylene S-aminoacrylic acid/ethylene maleic acid) (aminocarboxyl ratio of 1.0 to 3.0 described in Example 1). Stirring wascontinued for an additional 39 minutes. Throughout this period, duringwhich the temperature was held at 45 C., the well stabilized silverhalide emulsion grains remained entirely in suspension. By contrast,some sedimentation of silver halide emulsion grains was observed underthese same conditions if gelatin was used as the peptizer instead ofcopoly(ethylene B-aminoacrylic acid/ethylene maleic acid).

EXAMPLE 4 Copoly(ethylene B-aminoacrylic acid/ ethylene maleic acid),amino-carboxyl ratio of 1.0 to 5.0

This polymer was prepared in an identical manner to that in Example 1except that 31 g. of sodium azide was used. The isoelectricprecipitation occurs at pH 1.9 and 49 g. was collected.

Analysis: C, 47.7; H, 6.6; N, 3.7; Na, 3.

A neutral emulsion was prepared with this polymer as described inExample 1, except that stirring (at 70 C.) following completion ofsilver halide precipitation was continued for 30 minutes instead ofminutes. The emulsion obtained showed excellent stability and consistedof tabular octahedral crystals with diameters in the range 0.333.5microns.

EXAMPLE 5 An ammoniacal emulsion was prepared as described in Example 2,except that the peptizer used was copoly (ethylene B-aminoacrylicacid/ethylene maleic acid) (amino carboxyl ratio of 1.0 to 5.0)described in Example 4. The emulsion obtained showed excellent stabilityand consisted of cubic grains with diameters in the range 0.59-1.67microns.

EXAMPLE 6 Copoly(ethylene fi-aminoacrylic acid/ethylene maleic acid),amino-carboxyl ratio of 1.0 to 1.5

The procedure of Example 1 was followed except that intermediatemolecular weight copoly(ethylene maleic anhydride) and 62 g. of sodiumazide were used in the preparation. The isoelectric precipitation occursat pH 2.1 and the yield was 73 g.

Analysis: C, 44.3; H, 7.1; N, 7.5.

A neutral emulsion was prepared with this peptizer as described inExample 4. The emulsion obtained showed excellent stability andconsisted of tabular octahedral grains with diameters in the range0.5-3.3

microns.

EXAMPLE 7 An ammoniacal emulsion was prepared as described in Example 2with the medium molecular weight peptizer described in Example 6. Theemulsion obtained showed excellent stability and consisted of cubicgrains with diameters in the range 0.4-2.8 microns.

EXAMPLE 8 Copoly(ethylene fi-aminoacrylic acid/ethylene maleic acid),amino-carboxyl ratio of 1.0 to 1.5

The procedure of Example 1 was followed except that 126 g. ofcopoly(ethylene maleic anhydride) was used with 78 g. of sodium azide.The isoelectric point was approximately 3.5, and 40 g. of product werecollected.

Analysis: C, 47.9; H, 7.1; N, 8.5; NH 8.1.

6 A neutral emulsion was prepared with this peptizer as described inExample 4. The emulsion obtained showed excellent stability andconsisted of tabular octahedral grains with diameters in the range0.5-4.3

microns.

EXAMPLE 9 An ammoniacal emulsion was prepared as described in Example 2with the low-molecular-weight peptizer described in Example 8. Theemulsion obtained showed excellent stability and consisted of cubicgrains with diameters in the range 0.6-1.8 microns.

EXAMPLE 1O Copoly(ethylene B-aminoacrylic acid/ethylene maleic acid),amino-carboxyl ratio of 1.0 to 1.25

A solution of 126 g. of low-molecular-weight copoly (ethylene maleicanhydride) in 800 ml. of concentrated sulfuric acid was cooled to 8 C.in a five-liter 3-neck flask fitted with a stirrer, thermometer,nitrogen inlet and a drying tube. Sodium azide (97 g.) was added at sucha rate that the temperature remained between 8 and 12 C. After theaddition was complete, the solution was held at 8 C. for 16 hours, thenallowed to warm. The temperature rose to 40 C. spontaneously. When thetemperature started to fall, the solution was heated to C. for twohours, cooled and precipitated by pouring, in a fine stream, intoacetone, washed well with acetone and dried.

The polymer was dissolved in 800 m1. of water, diluted to 2 liters, andthe pH adjusted to 5.2 at which time the polymer reprecipitated. Theproduct was washed well with water, then acetone and dried. The yieldwas 65 g.

Analysis: C, 45.1; H, 7.2; N, 8.6; Na, .1.

A neutral emulsion was prepared with this peptizer as described inExample 4. The emulsion obtained showed excellent stability andconsisted of tabular octahedral grains with diameters in the range0.6-5.5

microns.

EXAMPLE 1 1 An ammoniacal emulsion was prepared as described in Example2 with the peptizer described in Example 10. The emulsion obtainedshowed excellent stability and consisted of cubic grains with diametersin the range 0.3-2.6 microns.

EXAMPLE 12 The different interaction effects, with the surface of silverhalide grains and during such development processes as physicaldevelopment, which may be obtained with copoly(ethylene fl-aminoacrylicacid/ethylene maleic acid) polymers of different amino/carboxyl ratios,were indicated by the following experimental results. Using the methoddescribed by E. J. Perry, Phot. Sci. Eng. 5, p. 349 (1961), the relative(i.e., compared to gelatin) rate of solution of silver halide solcrystals peptized by a given peptizer in a photographic developer, andthe relative rate of physical development at a constant silver ionconcentration supplied by a silver ion-thiosulfate complex in thepresence of the said peptizers were determined. The results obtainedwere as follows:

Polymer Relative Rate of Relative Rate of Amino] Molecular Solution ofPeptized Physical Development Carboxyl Weight Silver Halide at aConstant Silver Ratio Crystals Ion Concentration (Gelat1n=1.00)(Gelatin=1.00)

In the above table, low molecular weight refers to a startingcopoly(ethylene maleic anhydride) with a specific viscosity ofapproximately 0.1, and medium molecular weight refers to the samematerial with a specific viscosity of about 0.6.

The unexpected nature of our invention is demonstrated by the fact thatpolymers closely related to those of the invention fail to function assilver halide peptizers, as demonstrated in Examples 13 and 14.

EXAMPLE 13 A neutral emulsion was prepared as described in Example 1except that the peptizer used was copoly(ethylene ammonium maleamate).The emulsion obtained was completely unstable (i.e., the silver halidegrains were not peptized, but coagulated) EXAMPLE 14 An ammoniacalemulsion was prepared as described in Example 2, except that thepeptizer used was copoly (ethylene ammonium maleamate). The emulsion wascompletely unstable.

The copolymers useful as peptizers in accordance with our invention, maybe used in any of the methods previously described in the art whichrequire the use of a peptizer in the preparation of silver halidedispersions. The most useful molecular weights of the copolymersemployed in accordance with the invention correspond to the molecularweight range of polymers derived from copoly(ethylene maleic anhydride)of specific viscosities ranging from 0.1 to 0.6. However, useful resultsare obtained with copolyrners prepared from materials having specificviscosities of 0.02 to 1.0. The most useful ratio of polymeric peptizerto silver halide during emulsion precipitation extends fromapproximately 0.07:1 to 0.35:1. However, this concentration may bevaried over a considerable range as desired.

The silver halide grains precipitated in accordance with our inventionmay be washed and added to various vehicles, such as gelatin orsynthetic binders, e.g., polyvinyl alcohol or ethyl acrylate-acrylicacid copolymers, for coating purposes. Any precipitation technique, suchas those described in Photographic Emulsions by Wall, 1929, may beemployed using the copolymers of the invention.

The silver halide peptizers of the invention are useful in thepreparation of printout and direct-print emulsions as well as inemulsions of the developing-out type. The emulsions prepared with thesepeptizers may contain various silver halides, or combinations thereof,and may be utilized, e.g., in solvent transfer systems and color systemssuch as color films having incorporated-coupler systems and colorsystems in which the coupler is employed in developer solutions.Emulsions prepared using the subject peptizers may be sensitized withchemical or spectral sensitizers, such as those referred to in US.Patent 3,039,873, columns and 11.

The invention has been described in detail with particular reference topreferred embodiments thereof but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. In the method of preparing silver halide dispersions which comprisesprecipitating silver halide in an aqueous solution by reacting awatersoluble silver salt with a water-soluble halide salt, theimprovement which comprises incorporating in the aqueous solution, aspeptizer for the silver halide, a water-soluble polymer having a carbonchain backbone and comprising a plurality of recurring units havingamino and carboxyl groups, respectively, attached directly to respectiveadjacent carbon atoms in the polymer backbone.

2. In the method of preparing silver halide dispersions which comprisesprecipitating silver halide in an aqueous solution by reacting awater-soluble silver salt with a Water-soluble halide salt, theimprovement which comprises 8 -12 incorporating in the aqueous solution,as peptizer for the silver halide, a water-soluble polymer comprisingthe following repeating unit:

wherein Z is a divalent organic radical; A and Bare selected from thegroup consisting of amino and carboxyl; the ratio of amino groups tocarboxyl groups is from 1.0:5.0 to 1.0: 1.25; and in each repeatingunit, not more than one of A and B is an amino group.

3. In the method of preparing silver halide dispersions which comprisesprecipitating silver halide in an aqueous solution by reacting awater-soluble silver salt with a water-soluble halide salt, theimprovement which comprises incorporating in the aqueous solution, aspeptizer for the silver halide, a Water-soluble polymer comprising thefollowing repeating unit:

wherein A and B are selected from the group consisting of amino andcarboxyl; the ratio of amino groups to carboxyl groups in the polymer isfrom 1.0:5.0 to 1.0: 1.25; and in each repeating unit, not more than oneof A and B is an amino group.

4. A dispersion of silver halide in an aqueous solution of awater-soluble polymer having a carbon chain backbone and comprising aplurality of recurring units having amino and carboxyl groups,respectively, attached directly to respective adjacent carbon atoms inthe polymer backbone.

5. A dispersion of silver halide in an aqueous solution of awater-soluble polymer comprising the following repeating unit:

wherein Z is a divalent organic radical; A and B are selected from thegroup consisting of amino and carboxyl; the ratio of amino groups tocarboxyl groups is from 1.0:5.0 to 1.0:1.25; and in each repeating unit,not more than one of A and B is an amino group.

6. A dispersion of silver halide in an aqueous solution of awater-soluble polymer comprising the following repeating unit:

wherein A and B are selected from the group consisting of amino andcarboxyl; the ratio of amino groups to carboxyl groups in the polymer isfrom 1.0:5.0 to 1.0: 1.25; and, in each repeating unit, not more thanone of A and B is an amino group.

7. The method of preparing silver halide dispersions which comprisesreacting a water-soluble silver salt with a water-soluble halide salt inan aqueous solution of copoly(ethylene ,B-aminoacrylic acid-ethylenemaleic acid) having a ratio of amino-to-carboxyl groups within the rangeof l.0:5.0 to l.0:1.25.

8. In the method of preparing silver halide dispersions which comprisesprecipitating silver halide in an aqueous solution by reacting awater-soluble silver salt with a water-soluble halide salt, theimprovement which. comprises incorporating in the aqueous solution, aspeptizer for the silver halide, copoly(ethylene tI-aminoacrylicacidethylene maleic acid) having a ratio of amino-to-ca-rboxyl groupswithin the range of 1.0:5.0 to 1.0:1.25.

'9. In the method of preparing silver halide dispersions which comprisesprecipitating silver halide in an aqueous solution by reacting aWater-soluble silver salt with a water-soluble halide salt, theimprovement which comprises incorporating in the aqueous solution, aspeptizer for the silver halide, copoly(ethylene ,B-aminoacrylicacidethylene maleic acid) having a ratio of amino-to-carboxyl groupsWithin the range of 1.0:5.0 to 1.0:1.25, the ratio of said copolymer tosilver halide during the precipitation being within the range ofapproximately 0.07:1 to 0.35: 1.

10. A dispersion of silver halide in an aqueous solution ofc0poly(ethylene fi-aminoacrylic acid-ethylene maleic acid) having aratio of amino-to-carboxyl groups of from 1.0:5.0 to 1.0:1.25.

References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, PrimaryExaminer.

10 I. TRAVIS BROWN, Examiner.

R. H. SMITH, Assistant Examiner.

